The present invention relates to a record encoding system associated with recording media such as an optical disk and a magnetic disk and, more particularly, to a modulator and demodulator using a multilevel recording system.
For error-free reproduction of information recorded at a high density on a recording medium, various techniques have been studied thus far. Specific examples thereof include PRML (Partial Response Maximum Likelihood), DFE (Decision Feedback Equalizer), TCPR (Trellis Coding Partial Response), and the like. These techniques have been used for, e.g., signal processing LSIs for a hard disk apparatus.
Of the foregoing techniques, PRML uses a partial response (PR) scheme and a Viterbi decoding scheme which is one of maximum likelihood (ML) decoding schemes. The partial response scheme is a signal processing scheme which performs data reproduction by positively utilizing an intercode interference (interference between adjacent sets of data or between adjacent reproduced signals). The Viterbi decoding scheme is also termed a maximum likelihood data-sequence estimation scheme, which reproduces a most likely data sequence by using data of the past in a time sequence.
On the other hand, the introduction of new modulation codes is also observed. As representatives of the new modulation codes, there can be mentioned a rate 8/9 modulation code, a rate 16/17 modulation code, a (1, 7) RLL code, and the like. In the foregoing, RLL stands for Run Length Limited. In conventional systems, however, binary recording has been the main stream.
In recent years, optical disks such as a CD-R/W (Compact Disk Re-writable), a DVD (Digital Versatile Disk), and the like have been used widely and the recording densities thereof have been increased on a year-by-year basis. However, a conventional encoding efficiency has been 1 or less due to binary recording and a further increase in recording density cannot be expected under present circumstances.
It is therefore an object of the present invention to accomplish higher-density recording particularly on an optical disk.
To attain the object, the present invention provides a multilevel record modulator and demodulator having a function of converting a p-bit (p is an integer) binary data word to a q-symbol (q is an integer) multilevel code word such that multilevel recording on a recording medium is accomplished, the modulator and demodulator having: a look-up table for storing a modulation/demodulation table defining a correspondence between the binary data word and the multilevel code word; and a table generating circuit for receiving a plurality of parameters and generating the modulation/demodulation table to be stored in the look-up table such that each of constraints specified by the plurality of parameters is satisfied.